1. Field of the Invention
The present invention relates to a semiconductor device that drives and controls a high-potential-side power device of two power devices connected in series between a main power source potential of a high potential and a main power source potential of a low potential, and specifically, to a semiconductor device that can prevent the malfunction of power devices.
2. Background Art
FIG. 14 is a circuit diagram showing a half bridge circuit. Power devices 101 and 102, such as IGBT (insulated gate bipolar transistor), are totem-pole-connected between the positive pole and the negative pole (grounding potential, GND) of the power source PS. To power devices 101 and 102, free-wheel diodes D1 and D2 are connected in inverse-parallel, respectively. A load (inductive load, such as a motor) 103 is connected to the connecting point N1 of the power device 101 and the power device 102.
The power device 101 is a device that makes the potential at the connecting point N1 with the power device 102 a reference potential and performs switching operation between the reference potential and the power-source potential supplied by the power source PS, and is called a high-potential-side power device. On the other hand, the power device 102 that makes grounding potential a reference potential and performs switching operation between the reference potential and the potential of the connecting point N1, and is called a low-potential-side power device.
The power device 101 is driven by the high-potential-side power device driving circuit HD, and the power device 102 is driven by the low-potential-side power device driving circuit LD. To the high-potential-side power device driving circuit HD, a voltage VB of the anode of the high-potential-side power source 104 (high-potential-side floating power source absolute voltage) and a voltage VS of the cathode of the high-potential-side power source 104 (high-potential-side floating power source offset voltage) are supplied. The high-potential-side power device driving circuit HD outputs output signals HO to the gate electrode of the power device 102. Since the low-potential-side power device driving circuit LD is little related to the present invention, the description thereof will be omitted.
FIG. 15 is a circuit diagram showing a conventional semiconductor device. The semiconductor device is a high-potential-side power device driving circuit that drives and controls the high-potential-side power device of the two power devices connected between the main power source potential having high potential and the main power source potential having low potential in series.
Input signals HIN are given from an externally provided microcomputer or the like. Input signals HIN have “H (high potential)” (first state) that shows the conduction of a power device in the high-potential side, and “L (low potential)” (second state) that shows the non-conduction of a power device in the high-potential side.
A pulse generating circuit 11 generates pulsing ON signals (first pulse signals) and OFF signals (second pulse signals) corresponding to the level transition to “H” and “L” of input signals HIN, respectively.
The two outputs of the pulse generating circuit 11 are connected to gate electrodes of high breakdown voltage N-channel field effect transistors (hereafter referred to as HNMOS transistors) 12 and 13, which are level shift transistors, respectively. ON signals are given to the gate electrode of the HNMOS transistors 12, and OFF signals are given to the gate electrode of the HNMOS transistors 13. The drain electrodes of the HNMOS transistors 12 and 13 are connected to an end of each of resistors 14 and 15, and also connected to input terminals of inverters 16 and 17, respectively.
A level shift circuit is composed of the HNMOS transistors 12 and 13, resistors 14 and 15, and inverters 16 and 17. The level shift circuit shifts the levels of ON signals and OFF signals toward the high-potential side to obtain first and second level-shifted pulse signals, respectively.
An SR-type flip-flop circuit 19 inputs the output signals of the inverters 16 and 17 (first and second level-shifted pulse signals) via a protective circuit 18 from the set input terminal S and reset input terminal R, respectively. Here, the protective circuit 18 is a filter circuit for preventing the malfunction of the SR-type flip-flop circuit 19, and is composed of a logic gate.
The output terminal Q of the SR-type flip-flop circuit 19 is connected to the gate electrode of an NMOS transistor 20, and also connected to the input of the inverter 21. The output of the inverter 21 is connected to the gate electrode of an NMOS transistor 22. The voltage of the connecting point of the NMOS transistors 20 and 22 is outputted as an output signal HO in the high-potential side. By thus complementarily turning the NMOS transistors 20 and 22 ON and OFF, the power device 101 is switched.
The other ends of the resistors 14 and 15 are connected to the drain electrode side of the NMOS transistor 20, and a voltage VB is supplied. The source electrode of the NMOS transistor 22 is connected to the anodes of diodes 23 and 24 and the connecting point N1 shown in FIG. 14, and a voltage VS is supplied. The cathodes of the diodes 23 and 24 are connected to the drain electrodes of the HNMOS transistors 12 and 13, respectively.
Next, the operation of a conventional high-potential-side power device driving circuit will be described referring to the timing chart shown in FIG. 16.
First, the pulse generating circuit 11 generates pulse ON signals that transit to “H (high potential)” corresponding to the rise of input signals HIN. By the ON signals, the HNMOS transistor 12 is turned ON. At this time, OFF signals are in “L (low potential)”, and the HNMOS transistor 13 is in the OFF state.
Thereby, voltage drop occurs in the resistor 14 connected to the HNMOS transistor 12, and “L” signals are inputted into the inverter 16. On the other hand, since no voltage drop occurs in the resistor 15 connected to the HNMOS transistor 13, “H” signals are continuously inputted into the inverter 17. Therefore, the output signals from the inverter 16 become pulse signals that transit to “H”, and the output signals from the inverter 17 are maintained in the “L” state.
Then, the protective circuit 18 that has received output signals from inverters 16 and 17 outputs pulse signals that transit to “L” corresponding to the output signals from the inverter 16 into the set input terminal S of the SR-type flip-flop circuit 19. On the other hand, the protective circuit 18 outputs “H” signals corresponding to the output signals from the inverter 17 into the reset input terminal R of the SR-type flip-flop circuit 19.
The pulse generating circuit 11 generates pulse OFF signals that transit to “H (high potential)” corresponding to the fall of input signals HIN. In this case, the protective circuit 18 also performs the same operation as described above, and outputs “H” signals corresponding to the output signals from the inverter 16 into the set input terminal S of the SR-type flip-flop circuit 19. On the other hand, the protective circuit 18 outputs pulse signals that transit to “L” corresponding to the output signals from the inverter 17 into the reset input terminal R of the SR-type flip-flop circuit 19.
As a result, the output terminal Q of the SR-type flip-flop circuit 19 transits to “H” in the timing when ON signals are given, and transits to “L” in the timing when OFF signals are given. Furthermore, output signals HO obtained by complementarily turning the NMOS transistors 20 and 22 ON and OFF also become the same sort of signals.
A problem that arises here is dv/dt transient signals generated in the line from the connecting point N1 to the anodes of diodes 23 and 24 depending on the switching state of the half-bridge-type power device composed of power devices 101 and 102.
If dv/dt transient signals are generated, a dv/dt current obtained by the product of a parasitic static capacitance between the drains and sources of the HNMOS transistors 12 and 13 and the dv/dt transient signals simultaneously flows in the HNMOS transistors 12 and 13. Thereby, erroneous pulse by the dv/dt transient signals is simultaneously given instead of ON signals and OFF signals. In such a case, the protective circuit 18 is constituted so as to prevent simultaneous signal input into the SR-type flip-flop circuit 19 (for example, refer to Japanese Patent Application Laid-Open No. 9-200017).